1. Field of the Invention
The present invention relates to a method and an apparatus for forming zinc oxide. More particularly, the present invention relates to a cost-effective and environmentally friendly method and apparatus for forming zinc oxide.
2. Description of the Related Art
Zinc oxide is an important raw material used in many industries. Zinc oxide is a II-IV group ceramic material which has characters such as high chemical stability, a low dielectric constant, a high electromechanical coupling coefficient, photocatalytic property, and a large band gap. At present, micro-sized zinc oxide is widely used as an adhesion enhancing additive for tires. World demand for the micro-sized zinc oxides is more than six hundred thousand tons. Sub-micro-sized zinc oxide is primarily used for high performance aircraft tires. Meanwhile, it is known that nano-sized zinc oxides having properties such as surface effect, quantum size effect, uniform dispersion and high photocatalytic property, are completely different from micro-sized or sub-micro-sized zinc oxides having a particle size of more than 100 nm. In recent years, there have been breakthroughs in the application of the nano-sized zinc oxides in fields such as ceramics, chemical engineering, optics, electricity and medical, in which industrial value and growth prospects are greater than conventional micro-sized zinc oxides.
The conventional process of forming zinc oxide can be represented by a chemical equation: Zn+½O2→ZnO. The process is performed at a temperature of about 1000° C. by using heavy oils as fuels. This process is an open process which consumes huge amounts of energy and produces a lot of carbon dioxide. Often used methods for forming nano-sized zinc oxide include precipitation, homogeneous precipitation; spray pyrolysis and sol-gels processes. These methods all have their specific advantages, respectively, but all of them have the same problems of high cost and complex manufacturing. Therefore, a cost-effective and environmentally friendly method for forming zinc oxide is needed.
New environmentally friendly sources have been promoted due to global warming and high oil prices. Hydrogen energy is considered as one of a next generation of energy sources and its application in hydrogen fuel cells has been widely used to replace petroleum. Accordingly, hydrogen energy is expected to become the most popular energy source in future.
Thus, the commercial prospects for the formation of zinc oxides (or nano-sized zinc oxides) along with hydrogen energy sources are high. For example, U.S. Pat. No. 6,663,681 discloses a method for reducing a water vapor to hydrogen by metal catalysis. In this method, water vapor is introduced through a dipping pipe to contact with a mixture of molten reactive metals (iron and tin are the major constituents), and the reactive metals react with the oxygen atom of the water vapor to form metal oxide and hydrogen. However, because a dipping pipe is used to introduce the water vapor to the molten reactive metals, reaction area is limited. In addition, zinc oxide is not the major product of this reaction and nano-sized zinc oxides are not formed.
WO Patent Publication 2,006/114,034 discloses an electrolysis method for forming zinc oxide and hydrogen. In this method, zinc is used as an electrode for performing water electrolysis process. However, this method needs to consume huge amounts of electrical energy. Moreover, there is no effective method to separate the zinc oxide deposition from the electrolysis system and nano-sized zinc oxides are also not formed.
Therefore, a cost-effective and environmentally friendly method for forming zinc oxide along with hydrogen energy source is needed.